Goal:
  
  A : Type
  B : Type
  t : A
  P : B → A → A → Type
  b : B
  bs : list B
  hd' : A
  tl : list A
  p : P b t hd'
  e : #|bs| = #|tl|
  ============================
   (∑ i' : B, Some b = Some i' × P i' t hd')


DEBUG:Going to execute:
match reverse goal with
           | id:(?X1 → ?X2) → ?X3
             |- _ =>
                 Ltac.cut X3;
                  [ intro; clear id; t_tauto_intuit
                  | Ltac.cut (X1 → X2);
                     [ exact
                     id
                     | generalize (λ y : X2, id (λ x : X1, y)); intro; clear
                        id; (solve [ t_tauto_intuit ]) ] ]
           | id:¬ ?X1 → ?X3
             |- _ =>
                 Ltac.cut X3;
                  [ intro; clear id; t_tauto_intuit
                  | Ltac.cut (¬ X1);
                     [ exact
                     id
                     | clear id; intro; (solve [ t_tauto_intuit ]) ] ]
           | |- ?X1 =>
                 <Coq.Init.Tauto.is_disj> flags X1; (solve
                  [ Ltac.left; t_tauto_intuit | Ltac.right; t_tauto_intuit ])
           end